Copper has displaced aluminum to become the standard back-end-of-line (BEOL) metallization material for advanced logic devices. Copper's benefits over aluminum for logic are now well-documented. Its lower resistivity allows line thickness to be reduced by nearly one-third while achieving similar sheet resistance.
The formation of copper containing films via Chemical Vapor and Atomic Layer Deposition (CVD and ALD) are promising. Desirable properties of the copper precursor for these applications are: i) high volatility, ii) sufficient stability to avoid decomposition during handling and delivery, and iii) appropriate reactivity. For industrial process reasons, deposition of copper should be realized at low temperature, below 150° C., which makes deposition of copper particularly challenging.
PEALD and PECVD are promising techniques to produce high purity and high-density metal thin films at low growth temperatures.
E. Eisenbraun et al. J. Vac. Sci. Technol. B 25, 6, 2007 and Eisenbraun, E. Electrochemical and Solid-State Letters, 11, 5, H107-H110, 2008 describe the deposition of copper by PEALD using Cu(acac)2 and hydrogen as reductant. Continuous and pure films (95% purity) were obtained on TaN, SiO2 and Ru in a temperature range between 85 and 135° C. Moreover conformal depositions have been achieved over high aspect ratio (5:1) structures.
Until now, PEALD and PECVD have never been considered as possible for the deposition of pure copper with copper bis-ketoiminate precursors.